Process for producing highly crimped fibers having modified surfaces



Aprll 19, 1966 w, s u 3,247,300

PROCESS FOR PRODUCING HIGHLY CRIMPED FIBERS HAVING MODIFIED SURFACES Filed 001}. 25, 1.962

INVENTOR WILLIAM LESTER STUMP ATTORNEY United States Patent 3 247 300 rnocnss Fon rnonbcnto moms? caiMrEn FIBERS HAVING MODEFIED SURFACES William Lester Stump, Kinston, N.C., assignor to E. I. du Pont de Nernours and Company, Wilmington, Del,

a corporation of Delaware Filed 00. 25, 1962, Ser. No. 232,992 9 Claims. (Cl. 264-168) This invention relates to filaments and fibers of synthetic polymers which crimp spontaneously. More particularly it relates to the production of fibers having an unusually high level of crimp by a crack-drawing process which provides microscopic surface irregularities.

It is known to extrude molten synthetic linear organic polymer in the form of filaments, to quench the extruded filaments in an asymmetric manner immediately after formation to produce an asymmetric birefringence differential across the diameter ofthe filaments, and to orient the extruded filament by drawing so that the filament spontaneously crimps after release of the orienting tension or upon a relaxing treatment. The crimp is of a three-dimensional nature not possible by conventional mechanical crimping methods. Such crimped fibers are extremely useful, especially in the form of staple fibers and can be as stufiing materials and in the manufacture of bulky fabrics. The processes previously used have been able to produce only a limited amount of crimp in the fibers. For some applications it is desirable to have an even more highly crimped product.

It is an object of this invention to provide a drawing method for obtaining useful crimped fibers with an unusually high degree of crimp and a desirable modified surface from asymmetrically quenched fibers. Another object is to provide such highly crimped fibers which, in the unrelaxed condition, have a relatively low (30% or less) amount of shrinkage in boiling water. Other objects will become apparent from the specification and claims.

One object of this invention has been achieved by the improvement, in the process mentioned above, of'contacting the unoriented synthetic polymer filaments, characterized by an asymmetric birefringence differential across the diameter of the filaments, under tension with a cracking agent, then applying to the filaments a liquid medium free of cracking agent and drawing the wet filaments at a temperature below 80 C. to provide a substantially oriented structure. The crimp is developed in the wet drawn filaments by (a) drying the filaments under essentially tensionless conditions, or (b) drying the filaments under tension and thereafter hot-relaxing the filaments in an essentially tension-free condition.

Preferably, the drawing is conducted while the filaments are wet with a liquid medium at a temperature of about 20 to 50 C. The process is especially useful for treating filaments of a polyester linear condensation polymer.

The drawing is a schematic illustration of the process of this invention and apparatus suitable for use in the process.

Depending upon the asymmetric filaments treated, the cracking agent, the extent of draw and the drawing temperature, the substantially oriented filamentary products of this invention have from to 50 or even more helical crimps per inch of crimped filament length. The products are further characterized by microscopic bulges spaced from 1 to 10 fiber diameters apart along the filaments, i.e., at a frequency of about 100 to 1000 bulges per inch of filament. The bulges have a height above the basic filament diameter (D) of from 0.05D to 0.4D. The bulges may be located on only one side of a filament, or may extend partly or completely around the fiber.

3,247,300 Patented Apr. 19, 1966 They are substantially smooth when viewed under a microscope, without sharp edges such as the scale of natural fibers. The bulges are randomly located along the filaments, i.e., along any given filament and also on different fibers of the same bundle. These provide a desirable low coefficient of hydrodynamic friction of from 0.26 to 0.41, whereas typical smooth filaments have values of 0.68 to 0.75.

In an unrelaxed condition, the substantially oriented product of this invention has a shrinkage in boiling water of 3% to 30% (up to 10% for preferred forms), a tenacity of 1.5 to 3.5 grams per denier, an elongation at break of 10% to 40% and an initial modulus of 20 to 50 grams per denier. When the above product is relaxed; as in a scouring process or by heating in a tensionless condition at C.', the relaxed filaments have a shrinkage in boiling water of 0% to 2.0%, a tenacity of 1.5 to 3.0 grams'per denier, an elongation at break of 20% to 50% and an initial modulus of 15 to 40 grams per denier.

By the expression of uniform chemical composition is meant that the filament is composed of one or more components of uniform chemical composition along its length. The bulges are of the same polymer as the adjacent regions and are free from large particles of a foreign matter. The filaments may be composed of one polymer only or may be of a composite nature with two or more components of different polymers such as taught in Breen US. Patent No. 2,931,091, granted April 5, 1960.

By the expression substantially oriented is meant that all portions of the filament along its length have a birefringence of at least about /3 the maximum obtainable.

The products of this invention" display an improved processability such as a lower drafting tension in staple yarn spinning procedures. The products impart an increased bulk to fabrics and afford better covering power in fabrics than previously known fibers.

By the word diameter is meant the'avera'ge thickness of the filament transverse to its length. Filaments of non-round cross-section can be used.

The hydrodynamic friction coefficient is determined as follows:

A test filament is hung over a /2 inch diameter polished chrome-plated mandrel so that the filament contacts the mandrel over an arc of approximately A 0.3 gram weight is attached to one end of the filament (input tension) and a strain gauge is attached to the other end (output tension)- The mandrel is rotated at a speed of 1,800 y.p.rn. and the area of contact flooded with a drop of No. 50 mineral oil immediately before strain gauge readings are made. The coefiicient f is calculated from the belt friction equation:

1 where f is the coefficient of hydrodynamic friction, T is the input tension, T is the output tension, and a is the angle of wrap. In general, the invention can be used with any crystallizable thermoplastic polymer.

Because of their commercial availability, ease of processing and excellent properties, the condensation polymers and copolymers, e.g., polyarnides, polysulfonamides and polyesters and particularly those that can be readily melt spun are preferred for application in this method. Suitable polymers can be found for instance among the fiber-forming polyamides and polyesters which are described e.g., in US. Patents 2,071,250,

2,071,253, 2,130,523, 2,130,948, 2,190,770, 2,465,319, 2,658,055 and 2,676,945.

Polyamides may contain the repeating unit wherein X and Y represent divalent aliphatic or cyclo-ali-phatic groups and Z- represents the linkage as in polyhexamethylene adipamide, polycaproamide, and polypiperazine adipamide. The group Y may be replaced with a divalent aromatic radical (A) as in polyhexamethylene terephthalamide. Additionally, polyamides having repeating units such as is divalent alkaryl (such as xylylene) may be used.

In a preferred embodiment of the invention, the polyester polymer is a synthetic linear condensation polyester of bifuncti'onal ester-forming compounds wherein at least about 75% of the repeating structural units of the polymer chain include at least one divalent carbocyclic ring containing at least six carbon atoms present as an integral part of the polymer chain and having a minimum of four carbon atoms between the points of attachment of the ring in the polymer chain (para-relationship in the case of a single G-membered ring). The polyesters may be derived from any suitable combination of bifunctional ester-forming compounds. Such com-pounds include hydroxy acids such as 4-(2-hydroxyethyl)benzoic acid and 4-(2-hydroxyethoxy)benzoic acid, or mixtures of the various suitable bifunctional acids or derivatives thereof and the various suitable dihydroxy compounds and derivatives thereof. The repeating structural units of the polymer chain comprise recurring divalent ester radicals as in-chain linking units which are separated by predominantly carbon atom chains or rings comprising hydrocarbon radicals, halogen-substituted hydrocarbon radicals, and chalcogencontaining hydrocarbon radicals wherein each chalcogen atom is bonded to carbon or a different chalcogen atom, and no carbon is bonded to more than one chalcogen atom. 'Thus, the repeating units may contain ether, sulfonyl, sulfide, or carbonyl radicals. Sulfonate salt substituents may also be present in minor amount, up to about 5 mol percent total sulfonate salt substituents in the polyester based on the number of ester linkages present in the polyester. See, for example, U.S. Patent No, 3,018,272. Other suitable substitu'ents may also be present.

Among the various suitable dicarboxylic acids are terephthalic acid, bromoterephthalic acid, hexahydroterephthalic acid, 4,4'-sulfonyldibenzoic acid, 4,4'-diphenic acid, 4,4-benzophenonedicarboxylic acid, 1,2-bis- (4-carboxyphenyl)ethane, 1,2 bis(p-'carboxyphenoxy)- ethane bis-4-carboxyphenyl ether and various of the naphthalene-dicarboxylic acids, especially the 1,4-, 1,5-, 2,6-, and 2,7-isomers. Isophthalic acid is also suitable especially when used in combination with a 1,4-dihydroxyaromatic compound. Carbonic acid is similarly suitable.

Among the various suitable dihydroxy compounds are the glycols, such as ethyleiie "glycol and other glycols taken from theseries HO(CH) OH, where n is 2 to 10; cisor trans-p-hexahydroxylylene glycol; diethylene glycol; quinitol; neopentylene glycol; l,4-bis(hydroxyethyl)benzene; and 1,4 bis(hydroxyethoxy)benzene. Other suitable compounds include dihydroxyaromatic com-pounds such as 2,2-bis(4-hydroxy 3,5 dichlorophenyl)propane, hydroquinone, and 2,5- or 2,'6-dihydroxynaphthalene.

'A perferred manner to obtain the unoriented, asymmetrically birefringent starting filaments of this process is to extrude a molten polymer into filaments and quench the filaments asymmetrically by directing a jet of air against one side of the filaments as they emerge from the spinneret orifice to produce solidified filaments having a differential birefringence across the diameter of the filaments, as can be determined by examination under a polarizing microscope. More preferably, the spinning conditions of French ,Patent No. 1,257,932 dated February 27, 1961, are used where the air quench is applied within one inch of the spinneret face so that the velocity of the air striking the filaments is at least about 850 feet per minute. Generally, it is convenient to use air at 15 to 30 C. The specific conditions for any one polymer can readily be determined by one skilled in the art and are not a part of this invention. Satisfactory as-spun filaments are further characterized by a relatively low order of orientation so that they can be drawn in the process.

By the expression cracking agent is meant any liquid which will cause cracks to form on the surface of the fiber when tension is applied. This phenomenon is well known and is not a part of this invention. A simple test for a cracking agent may be done by stretching a freshlyspun, undrawn fiber under the surface of the candidate liquid beyond the yield point of the fiber, i.e., to about 1.1 times its original length. Microscopic examination of the fiber will show transverse cracks and multiple necks characterized by diameters smaller than the remainder of the fiber if the candidate liquid is a suitable cracking agent. By freshly-spun is meant a fiber that is less than about one week old. Another characteristic of a cracking agent is that the force for a given stretch in a cracking liquid is always measurably lower than the force for the same stretch in air under the same stretching conditions. This cracking step generally occurs at temperatures below about 50 C. and, preferably, the cracking agent is effective at about room temperature, i.e., about 20 to 30 C.

Suitable cracking agents for use with polyester fibers include kerosene (distilled to give boiling range of 154 to 255 C.), dimethoxyethane', progargyl alcohol, N-vinyl pyrrolidone, homologous alkyl benzenes, alcohols,- acids, esters, ketones, and olefinic compounds.

The following compounds are particularly useful as cracking agents in the form of aqueous solutions with polyester fibers: pyridine, 2-methy1 pyridine, dimethyl pyridine, 4-methyl pyridine, 3-methyl pyridine, 2,4-dimethyl pyridine, ethanol and benzyl amine with the ac tivity of theagents increasing in the order given.

The drawing step may be done in any convenient manner and through heated mediums, over pins, rolls, hot plates, etc., and the like as long as the temperature of such mediums or surfaces is kept at C. or below. Preferably, thedrawing is conducted in a liquid medium such as a bath or spray where the temperature is readily controlled.

In general, the fibers will be drawn to between 2.3 and 3.5 times their length before drying.

The greatest crimp intensity is obtained When the entire drawing process is done with the fibers in contact with the cracking agent.

Following drawing the filaments may be cut to staple length fibers or further processed as continuous filaments.

The final products are characterized by the number of crimps per crimped inch. This is determined by counting the number of undulations in a length of fiber and dividing by the length of the fiber as measured under no tension. The number of undulations divided by the length as measured when under sufficient tension to just remove all crimps is the crimps/extended length.

The drawn fibers may immediately develop the high degree of helical crimp characteristic of the products of this invention or, depending on the cracking agent employed, it may be necessary to completely remove any trace of the cracking agent in the fiber as, for example, by drying in order to develop the crimp. This drying step should be conducted with the fibers in an unrestrained (relatively tensionless) condition and may be done at temperatures of 25 to 200 C. are dried under tension (as when'on a package of yarn) a relaxation at an elevated temperature (e.g., C.)

under essentially tensionless conditions is required to clevelop the crimp. This method affords crimp frequency If the fibers.

equivalent to that obtained by crimping through drying under tensionless conditions.

Example 1 This example shows the preparation of the fiber for the process of this invention. A condensation polyester, poly[ethylene glycol terephthalate/S-(sodium sulfo)isophthalate] (98/2 mole percent) having a relative viscosity of 15.5 in a mixture of phenol/trichlorophenol (5 8.8/ 41.2 weight ratio) is extruded from a melt through a spinneret maintained at a temperature of 275 to 280 C. The polymer is extruded at the rate of 0.288 gram per minute per hole. The spinneret contains 169 orifices of 0.010 mil diameter spaced in 13 rows having 13 holes per row in a square pattern so that the distance between adjacent orifices (center to center) is 60 mils. A stream of air at a temperature of about 20 C. at a velocity of about 1700 feet per minute is directed against the filaments as they emerge from the spinneret through a nozzle of square cross-section that is 1.25 inches on the side, located /2 inch distance from the filaments and A1 inch below the spinneret. The solidified filaments are wound up at 400 yards per minute as a 1200 denier yarn.

The individual as-spun filaments exhibit an asymmetric Example 2 This provides comparisons with the claimed embodiment of the invention.

A number of ends of the fibers prepared in Example 1 are combined to a tow having a denier from 10,000 to 20,000 denier and drawn on an apparatus of the type illustrated in the drawing. The tow 17 of as-spun fibers is advanced by feed rolls 1, 2, 3 and 4 at 33 yards per minute (y.p.m.) into vessel 18, containing undiluted 2B denatured ethyl alcohol as a cracking bath at about 25 C., and is drawn to a length 2.54 times its as-spun length (i.e., 2.54X draw ratio) by draw rolls 5, 6, 7, 8, etc., operating at about 84 y.p.m. The spray nozzles 19 are not used. The drawn tow is collected and dried at room temperature under essentially tensionless conditions. The individual filaments of the tow spontaneously crimp as they dry to the extent of 29 to 46 crimps per inch of crimped length (20-31 crimps per inch of extended length). The crimped filaments have a tenacity of 1.5 grams per denier, an elongation at the break of 28%, and a shrinkage on boil-off of only 3.4% (Item A). When viewed under a microscope, the filaments display a rough surface due to the presence of bulges ranging in height from 0.1 to 0.4 the fiber diameter and occurring at 1 to fiber diameters apart. On many of the fibers the bulges occur on only one side of the fiber. On some fibers the bulge appears to be symmetrically disposed about the fiber axis. The coefficient of hydrodynamic friction is 0.310.

After hot-relaxing in an essentially tensionless condition at 140 C. for 6 minutes, the 3.5 denier per filament fibers have the same crimp and rough surface as before but now have a tenacity of 1.7 g.p.d., an elongation of 35%, an initial modulus of 21.4 g.p.d. and a shrinkage in boiling water of less than 1%. This combination of very high crimp level and rough surface provides increased cover and increased bulk in fabrics made from these fibers.

When the undiluted denatured ethyl alcohol is re placed with a 25% aqueous solution of ethanol (at 25 C.), and the tow is drawn 2.71X and dried as before, the dried (but otherwise unrelaxed) product contains from 27 to 38 crimps per inch, has a tenacity of 2.0 g.p.d., an elongation at the break of 33% and shows a boil-off shrinkage of 22.6% (Item B).

As a control, the tow is drawn in a conventional manner using the same apparatus, but with no bath in vessel 18, rolls 18 being operated at the same surface speed as feed rolls, and using spray nozzles 19 to apply finishing agent during drawing. The tow is forwarded by feed rolls 1-8 at 33 y.p.m. through a C. spray from nozzles 19 of an aqueous solution of a textile finishing agent, comprised primarily of diethanolamine and triethanolamine salts, and drawn 3.33X by draw rolls 9-16. After drying as before, the filaments of this tow contain only 9 crimps/inch and have a boil-off shrinkage of 9.8% (Item c Equivalent results to Item A are obtained when the polymer is replaced with poly(ethylene terephthalate) itself, poly(ethylene 2,6-naphtha1ene dicarboxylate) and 'poly(ethylene terephthalate/hexahydroterephthalate) 90/ 10 mole ratio.

The ethyl alcohol can be replaced with 10% aqueous pyridine, 10% aqueous dimethoxyethane, 30% aqueous dioxane, cyclohexane, purified kerosene, and tertiary butyl alcohol to give results equivalent to Item A.

Example 3 A tow prepared as in Example 1 is forwarded by feed rolls 1-8 at a speed of 14 y.p.m. through a bath of undiluted ethanol invessel 18 and drawn 2.38X by draw rolls 916 in a spray from nozzles 19 of the aqueous finishing agent of Example 2 (Item C) at 50 C., and then dried under essentially tensionless conditions. The drawn, dry filaments have 19.0 crimps/inch, a tenacity of 1.0 gram per denier, an elongation of 29%, a modulus of 39 g.p.d., and 23% boil-off shrinkage. The product roughness is about the same as Item A of Example 2. The coefficient of hydrodynamic friction is 0.278.

It is surprising that the brief exposure under tension to a cracking agent followed by drawing under conditions where the agent would be presumably removed by the aqueous spray affords a significantly higher level of crimp than the control (Item C of Example 2). Omission of the ethanol bath produces a product with a boil-off shrinkage of 65% which is of little value in normal textile operations. Also, the tow cannot be drawn satisfactorily in the absence of the cracking agent at spray temperatures of less than about 65 C. because of the large number of broken filaments which limits the process and the poor fiber properties obtained.

When the temperature of the spray is raised to 80 C. in the above process, the dry drawn filaments have 10 crimps/inch and a boil-off shrinkage of 26%. The use of spray temperatures above 80 C. in the above procedure affords a smaller amount of crimp and a marked reduction in the surface roughness of the fibers.

It will be understood that the exact level of crimp obtained by prior art processes and this process will depend upon the particular polymer used and the spinning conditions. In general, the process of this invention affords a crimp level expressed as crimps per crimped inch of from 1.5 to 6 times or more than obtained by drawing the same as-spun fiber in a conventional process. The products contain from 15 to 50 or more crimps per inch of crimped length.

Since many different embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited by the specific illustrations except to the extent defined in the following claims.

I claim:

1. In the process of producing crimped filaments by extruding molten synthetic linear organic polymer in the form of filaments followed by asymmetric quenching to produce unoriented filaments having an asymmetric birefringence differential across the diameter of the filaments, and then drawing the filaments to provide a substantially oriented structure, the improvement for producing filaments characterized by a high crimp and a low coefiicient of hydrodynamic friction which comprises contacting the unoriented, asymmetrically birefringent filaments under tension with a cracking agent, then applying to the filaments a liquid medium free of cracking agent and drawing the wet filaments at a temperature below 80 C. to provide a substantially oriented structure having the property of spontaneously developing from 15 to 50 crimps per inch of filament under'- esse ntially tensionless conditions.

2. A process as defined in claim 1 wherein the wetdrawn filaments are dried under essentially tensionless conditions to provide filaments having from 1-5 to 50 crimps per inch.

3. A process as defined in claim 1 wherein the wetdrawn filaments are dried under tensionand the filaments are then hot-relaxed in an essentially tensionless condition to provide filaments having from 15 to 50 crimps per inch.

4. A process as defined in claim 1 wherein the unori ented, asymmetrically birefringent filaments are drawn while wet with aqueous medium at about 20 to 50 C.

5. A process as defined in claim 1 wherein the filaments are formed of a polyester synthetic linear condensation polymer. I

6. A process as defined in claim 5 wherein the polyester is an ethylene glycol terephthalate polymer.

7. A process as defined in claim 1 wherein the unoriented, asymmetrically birefringent filaments are formed by extruding the molten polymer through spinneret orifices and quenching the filaments by directing a jet of air against one side of the filaments within one inch of the spinneret orifices.

8. A process as defined in claim 1 wherein the unoriented, asymmetrically birefringent filaments are drawn in a liquid medium to between 2.3 and 3.5 times their length and then dried.

'8 9. A process as defined in claim 1 wherein the cracking agent is selected from the group consisting of ethyl alcohol, aqueous pyridine, aqueous dimethoxyethane, aqueous dioxane, cyclohexane, kerosenefand tertiary butyl alco- 5 hol.

References Cited by the Examiner l V UNITED STATES PATENTS 2,377,810 6/1945 Robbins 264-168 2,517,694 8/1950 Merion et al 28-82 2,715,763 8/1955 Marley 28-82 2,730,758 1/1956 Morrelletal 264-178 2,734,794 2/1956 Calton 264--168 2,811,410 10/1957 Munch et a1 18-54 2,875,502 3/1959 Mathews et a1. l8-54 2,918,347 12/1959 Notarbartolo et al. 1854 3,050,821 8/1962 Kilian 264168 3,102,323 9/1963 Adams -2 264--290 20 3,117,173 1/1964 Adams 264210 3,134,833 5/1964 Ciporin etal -1--- 2642l0 OTHER REFERENCES Woods & Hookway: Journal of the Textile Institute,

vol. 46, No. 9, September 1955, pp. 1629-1631, published 0 ROBERT F. WHITE, Primary Examiner.

WILLIAM STEPHENSON, ALEXANDER BRODMER KEL, Examiners. 

1. IN THE PROCESS OF PRODUCING CRIMPED FILAMENTS BY EXTRUDING MOLTEN SYNTHETIC LINEAR ORGANIC POLYMER IN THE FORM OF FILAMENTS FOLLOWED BY ASYMMETRIC QUENCHING TO PRODUCE UNORIENTED FILAMENTS HAVING AN ASYMMETRIC BIREFRINGENCE DIFFERENTIAL ACROSS THE DIAMETER OF THE FILAMENTS, AND THEN DRAWING THE FILAMENTS TO PROVIDE A SUBSTANTIALLY ORIENTED STRUCTURE, THE IMPROVEMENT FOR PRODUCING FILAMENTS CHARACTERIZED BY A HIGH CRIMP AND A LOW COEFFICIENT OF HYDRODYNAMIC FRICTION WHICH COMPRISES CONTACTING THE UNORIENTED, ASYMMETRICALLY BIREFRINGENT FILAMENTS UNDER TENSION WITH A CRACKING AGENT, THEN APPLYING TO THE FILAMENTS A LIQUID MEDIUM FREE OF CRACKING AGENT AND DRAWING THE WET FILAMENTS AT A TEMPERATURE BELOW 83*C. TO PROVIDE A SUBSTANTIALLY ORIENTED STRUCTURE HAVING THE PROPERTY OF SPONTANEOUSLY DEVELOPING FROM 15 TO 50 CRIMPS PER INCH OF FILAMENT UNDER ESSENTIALLY TENSIONLESS CONDITIONS. 